<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        div::after{
            content: '';
            border-top: 10px solid transparent;
            border-right: 10px solid transparent;
            border-bottom: 10px solid #333;
            border-left: 10px solid #transparent;
        }

    </style>
</head>
<body>

</body>
</html>